Sorry, I was out of town for a few days.
You should be able to accomplish this task without rebuilding the server. Make sure you backup everything first.
Power off the server, insert the new hard drive.
Using the compaq smartstart cd, you should be able to change the RAID to RAID5. This should automatically see the additional space and expand the array and allocate it accordingly. I'm assuming that all the drives are the same size.
Say you have 2-18.2gb drives now that are mirrored. If you inserted another 18.2gb drive and set it to RAID 5, you will double your usable space to 36.4GB.
The only thing I'm not completely sure about is how it handles the logical drive. I believe that the logical drive you currently have will remain intact. You will need to create another logical drive to use the rest of the space. Then you can create new volumes or span the volumes within netware (Assuming you're using Traditional volumes.. NSS is a little different)..
Compaq also has an NLM that can accomplish much of the same tasks without taking the server down.. CPQONLIN.NLM. load it from the console. I've had trouble expanding and resizing RAID's from there though, so i always use smartstart.
Let me know if that makes sense or if you have any further questions. Hope this helps and is not too late.
Marvin
Marvin Huffaker MCNE, CNE
Marvin Huffaker Consulting